The process of drilling hydrocarbon wells results in many wells with small diameter tubing or casing in the hydrocarbon bearing zone due to problems encountered during drilling and more casing strings being installed than were originally anticipated. Each string of casing is inherently smaller in diameter than the previously installed string to allow the successive casing string to be installed through the previous casing strings. For whatever the reason, many wellbores exist with casing in the hydrocarbon bearing zone with a diameter of less than three inches. When these wells are producing some amount of gas, the flow rate is sufficient to entrain and carry the liquids with the gas to the surface. Eventually, these slim holes mature to the point that the gas flow rate is not sufficient to carry the liquids to the surface. At the same time, there is still enough gas in the formation to continue to provide an economic incentive to keep the well open and producing.
Typically, some have installed coiled tubing that has a much smaller diameter than the small diameter casing to use the same gas productivity in the well to flow upwardly at a faster rate and keep the liquids entrained with the gas. This may work for a while, but the productivity of gas wells eventually diminishes to a point where it must be shut in.
In an ideal world, production tubing would be installed and a rod pump installed to positively pump the liquids from the bottom of the well and allow gas production to continue for the longest potential time and greatest potential recovery. However, many slim holes are not large enough to accommodate production tubing in which a rod pump can operate.